Abstract

Abstract

A method applied previously to Plasmodium falciparum was applied to P. vivax to study the maturation of asexual erythrocytic forms of P. vivax in vitro and the effects exerted by chloroquine upon such maturation. Detailed studies were carried out in an effort to translate morphological observations into quantitative data and to identify particular morphological features that might be useful as indices of maturation and inhibition. With this experimental system, 1) asexual erythrocytic forms of P. vivax underwent maturation in vitro; 2) chloroquine added in vitro inhibited this maturation; 3) findings after incubation depended in substantial part upon the maturity of the asexual parasites present at the outset of incubation; 4) no single morphological feature or endpoint served as a consistently satisfactory indicator of maturation and inhibition; and 5) relationships between concentrations and effects of chloroquine were at times inconsistent or erratic, particularly when the asexual parasites present at the outset of incubation consisted mainly of late ameboid forms rather than early ameboid forms or ring forms. Although this experimental system may be of value as a means for assessing the effects of chloroquine upon P. vivax in vitro under some circumstances, it appears that—in terms of simplicity of quantitative assessment and interpretation, reliability, and validity—this system may be considerably less useful or satisfactory when appled to P. vivax than when applied to P. falciparum from man.